This invention relates to systems and methods for forming a single crystal semiconductor film on a non-crystalline (e.g., an amorphous) surface.
Many different methods have been developed for forming single crystal epitaxial semiconductor films. Epitaxy is the regularly oriented growth of a crystalline substance on a crystalline surface. Single crystal films frequently have superior properties relative to other kinds of films, such as polycrystalline and amorphous films. Homoepitaxy is the growth of a crystalline film on a crystalline surface of the same substance. Heteroepitaxy is the growth of a crystalline film on a crystalline surface of a different substance. Chemical vapor deposition (CVD) processes, and to a lesser extent, physical vapor deposition processes, commonly are used to grow or deposit single crystal semiconductor layers on a crystalline substrate. The quality of the single crystal epitaxial films depends upon a number of different factors, including good lattice match between the film and the substrate, proper growth temperature, and proper reactant concentrations.
For many applications, polycrystalline or amorphous films are acceptable or even more desirable than epitaxial films. For example, many protective films are polycrystalline films, which may be characterized by high hardness, high corrosion resistance, and high oxidation resistance. Amorphous films (e.g., oxides, nitrides and glasses, such as silicon dioxide) also serve a number of useful functions, including electronic passivation, insulation and dielectric functions. Current device performance requirements, however, require that most or all of the active devices of an integrated circuit be formed in a single crystal semiconductor region. This requirement typically limits the integrated circuit devices to two-dimensional structures on a substrate surface.
Numerous attempts have been made to extend semiconductor device fabrication techniques to three-dimensional structures by growing single crystal films over amorphous films used as insulators in two-dimensional integrated circuits. For example, U.S. Pat. No. 4,686,758 describes a localized overgrowth process, in which seeding from a single crystal silicon substrate is used to grow single crystal silicon layers over an amorphous silicon dioxide gate layer. The localized overgrowth process involves etching a window in the silicon dioxide layer down to the single crystal silicon substrate, and growing an epitaxial silicon film upwardly from the substrate in the window. Localized overgrowth of single crystal silicon occurs when the selective epitaxial growth reaches the top surface of the silicon dioxide window. U.S. Pat. No. 6,103,019 describes a method of forming a single crystal film from a seed layer implanted in a non-crystalline surface by high-dose implanting of a nucleating species through a single crystal mask having appropriate channeling directions spaced at desired lattice constants. In zone melting recrystallization processes, a single crystal semiconductor layer may be formed on an amorphous layer by depositing a polycrystalline or amorphous semiconductor layer, melting the deposited layer with a laser or other energy source, and allowing the melted layer to re-crystallize, randomly or from a seed, by superposing a temperature gradient. Still other single crystal forming processes have been proposed.
The invention features a novel single crystal semiconductor film formation method in which a template layer is deposited onto a non-crystalline surface to serve as a seed layer for the subsequent epitaxial growth of a single crystal semiconductor film.
In one aspect, the invention features a method of forming a single crystal semiconductor film on a non-crystalline surface. In accordance with this inventive method, a template layer incorporating an ordered array of nucleation sites is deposited on the non-crystalline surface, and the single crystal semiconductor film is formed on the non-crystalline surface from the ordered array of nucleation sites.
As used herein, the phrase xe2x80x9cforming a single crystal semiconductor film from an ordered array of nucleation sitesxe2x80x9d refers broadly to the transfer of ordering information from the nucleation sites to the single crystal film being deposited.
Embodiments of the invention may include one or more of the following features.
The template layer preferably comprises an ordered array of organic molecules. The organic molecules may incorporate an inorganic species defining the ordered array of nucleation sites. The inorganic species may comprise one or more components of the single crystal semiconductor film. In some embodiments, the template layer is a Langmuir-Blodgett film. In one embodiment, the template layer comprises a close-packed matrix of polymerized organic monomers each incorporating one or more silicon atoms, and the single crystal semiconductor film is an epitaxial silicon film.
The template layer may include one or more monolayers deposited on the non-crystalline surface. The deposited template layer may be processed to expose the ordered array of nucleation sites. The template layer may be processed, e.g., by heating, to remove one or more volatile components of the template layer.
The template layer may deposited by a Langmuir-Blodgett deposition process, or by an evaporation-based deposition process.
The single crystal semiconductor film may be formed by a vapor phase deposition process, a solid-state crystallization process, or a zone melting recrystallization process.
A non-crystalline layer may be formed over the single crystal semiconductor film, and a second template layer incorporating an ordered array of nucleation sites may be deposited on the non-crystalline layer. A second single crystal semiconductor film may be formed from the ordered array of nucleation sites of the second template layer.
In another aspect, the invention features an integrated circuit, comprising a single crystal semiconductor layer formed from an ordered array of nucleation sites defined by an array of organic molecules disposed over a non-crystalline layer.
Among the advantages of the invention are the following.
The invention provides a method of forming single crystal semiconductor films of any desired orientation on an amorphous layer. This feature enables high quality, vertically integrated semiconductor devices (e.g., complementary meta-loxide semiconductor (CMOS) devices) to be fabricated. The invention therefore provides an alternative process for developing high density and high performance three-dimensional integrated circuits. In addition, the invention enables large area single crystal semiconductor films to be grown on amorphous glass substrates that may be used to produce, for example, high efficiency solar cells or components of displays.